Probes

Unmanned probes have been a mainstay of our endeavors to acquire information and understanding of
the distant planets and other objects in the Solar System. They are relatively
cheap to put into space and do not put human lives at risk.

There are many different types of probe, and some satellites that orbit
Earth can be considered probes, but the first probes we sent out beyond
Earth's gravitational pull were the Soviet (Russian) 'Lunik' class of
spacecraft, starting with 'Lunar 1' in 1959, that were sent to the Moon
during the late 1950's and early 1960's.

Voyager - on a mission out of the Solar System

The first probe to another planet was the American Mariner 2, which sent
back information about Venus. The first probe to leave the Solar System was
Pioneer 10 in 1983.

There have been probes sent to orbit Mercury, investigate Pluto, land on a
comet and to explore the asteroid belt. All these probes and many more have
gathered much important scientific knowledge about our Solar System that
would have not been possible with expensive, manned, spacecraft.

Kepler Mision

The Kepler telescope was launched on 7th March 2009. Its three and a
half year mission was to discover planets orbiting stars in a specific
portion of the galaxy. Just over four years later mechanical failure of
two reaction wheels, the mechanism used to accurately point the
telescope at the right point, has possibly ended the mission but not
before discovering over 130 planets and over 2,700 potential planets.
Read more about Kepler.